Purification of ethylene



Patented Feb. 14, 1950 PURIFICATION OF ETHYLENE Franklin S. Chance, Jr., Wilmington, Del, a!-

signor to E. I. du Wilmington, Del.,

Pont de Nemours & Company,

a corporation of Delaware No Drawing. Application April 18, 1946, Serial No. 663,233

(Cl. 26H") Claims. 1

This invention relates to gas separation processes and more particularly to a process for the separation of ethylene from mixtures containing ethylene and hydrocarbon impurities such as acetylene.

Numerous attempts have been made heretofore to separate ethylene from admixture with acetylene and similar unsaturated lnrdrocarbon gases which are generally present in crude ethylene obtained by pyrolytic reactions or by fractionation of coke oven gas. In U. S. Patent 2,250,925 a process is described for the separation of acetylene from gaseous mixtures containing ethylene by means of high pressure extraction with acetone followed by recovery of absorbed gases from the solvent at somewhat lower pres sure and recovery of the acetone by water scrubbing. While this patented process is efiective in that it reduces the acetylene content to about 0.01%, it has numerous disadvantages, e. g., it requires the use of a large number of pumps and other equipment which renders the process relatively expensive. Numerous alternative processes also have been disclosed. For example, acetylene has been removed from ethylene by means of selective solvents such as dimethyl formamide (U. S. 2,146,448), or certain esters, polyketones, lactones, and the like (U. S. 2,063,680 and U. S. 2,383,551). In general, these latter methods were not effective for the reduction of the concentration of acetylene to below a few hundredths of a percent.

An object of this invention is to provide an improved method for the separation of purified ethylene from mixtures containing ethylene, acetylene, etc. A further object is to provide a method for reducing the acetylene content of impure ethylene to below about 100 parts per million. Other objects and advantages of the invention will appear hereinafter.

These objects are accomplished in accordance with this invention by subjecting impure ethylene to the action of a dispersion of metallic sodium in a hydrocarbon medium as hereinafter described. In a specific embodiment the invention contemplates the removal of acetylene from impure ethylene by passing the said impure ethylene through a dispersion of metallic sodium in a hydrocarbon medium comprising tetrahydronaphthalene and naphthalene. The invention also includes the discovery that the efllciency 0f the removal of impurities such as acetylene from ethylene by means of metallic sodium is markedly improved by the use of metallic mercury in combination'with the metallic um. While the invention is primarily directed to the removal of acetylene from ethylene, other impurities, such as oxygen, water, alcohols, sulfur compounds, etc., may simultaneously be removed from ethylene in the practice of the invention.

thalene are especially suitable.

It has been disclosed heretofore (German Patent 494,575) that a dispersion of metallic sodium or potassium in boiling xylene, upon treatment with acetylene, gives sodium acetyllde. The present applicant has found, however, that at temperatures of about C. metallic potassium is very rapidly consumed by ethylene containing minute concentrations of acetylene, evidently due to a reaction between ethylene and potassium. It is therefore, rather remarkable that metallic sodium, under the conditions hereinafter set forth, is not consumed by the ethylene, but is highly eflective as a reagentin the purification of ethylene. The discovery that the acetylene concentration in fractionated ethylene can be reduced to below parts per million by treating such ethylene with metallic sodium is believed to be highly novel and surprising. It is even more surprising to discover that metallic mercury is effective as an agent to improve the process whereby acetylene is removed from impure ethylene by reaction with metallic sodium.

In the purification of ethylene in accordance with the present invention it is entirely possible that numerous reactions take place other than the formation of sodium acetylide. In fact it is observed that the hydrocarbon medium, while being used in the practice of the invention, acquires a markedly increased viscosity, which indicates a formation of soluble products which may be polymeric in nature. It is possible that hydrocarbon impurities which are not completely removed by fractionation of ethylene may either react with ethylene in the presence of metallic sodium, or may polymerize under the conditions employed. It is possible that to a certain extent acetylene may react with ethylene under these conditions. The metallic sodium may react to some extent with hydrocarbon medium, especially when the latter contains naphthalene. The applicant does not wish to be bound by any theory as to what takes place during the separation of impurities from crude ethylene in accordance with the invention since the important point is that by practicing the invention ethylene of a very markedly high degree of purity may be obtained.

The hydrocarbon media'which may be employed in the practice of the invention include tetrahydronaphthalene and other hydrocarbons which are liquid under the reaction conditions. Liquid hydrocarbon mixtures, in which one or more of the components may be a dissolved solid hydrocarbon are entirely satisfactory. Alkyl benzenes and alkyl naphthalenes may be employed if desired; Mixtures of tetrahydrcnaphthalene with solid hydrocarbons such as naph- The hydrocarbon solvents exert a somewhat selective action in the practice of the invention, and it has been observed that certain cyclic hydrocarbons, especially ,tetrahydronaphthalene-naphthalene mixtures are much more effective than straight chain hydrocarbons, kerosene, etc. Small amounts of higher polycyclic hydrocarbons such as anthracene may be employed as foam inhibitors if desired. Inert materials other than hydrocarbons (dioxane, aniline, etc.) may be present in the acetylene-removing agent, but such materials generally are neither necessary nor desirable.

. f'il'he dispersions of metallic sodium in hydro carbon media may be prepared by known methods, such as by rapidly stirring a mixture of moltensodlum suspended in the boiling hydrocarbon followed by cooling the mixture to solidify the while in the dispersed state. The preferned dispersions containing metallic sodium and mercury may be obtained quite readily by first preparing a dispersion of metallic sodium in the hydrocarbon media, and thereafter addin the desired quantity of mercury thereto, with stirring.

The invention is generally practiced at temperatures of about 30 to 150 C. The critical optimum temperature depends upon the other reaction conditions, and is frequently within the range of about 70 to 110 C.

The invention is illustrated further by means oi the following examples.

Example 1.-Ethylene containing 0.1% acetylene was passed through a dispersion containing about 25% metallic sodium in about 275 grams of monoamyl naphthalene at a temperature of 100 to 110 C. Some foaming was observed. A small amount of anthracene was added which inhibited this foam. Acetylene removal was complete when the gas rate was 0.4 ft./min. When the gas rate was increased to 0.9 ft./min. the gas contained 20 parts per million of acetylene.

Example 2.The following table illustrates the efi'ect of mercury upon the removal of acetylene from ethylene by means of metallic sodium dispersed in naphthalene-tetrahydronaphthalene mixture. In each of the experiments the weight of tetrahydronaphthalene employed was 275 rams.

Efiect of Hg in sodium-naphthalene-tetmhydronaphthalene system upon removal of acetylene from ethylene Wt. Naph- P. P. M. Wt. Hg, Wt. Na, 'lemp., Gee

grams grams gi g 0. Rate fsg ag Untreated gas 1,725

It is to be understood that the foregoing exam-. ples do not limit the invention but are illustrative only. Many methods of practicing the invention will occur to those who are skilled in the art. For example, numerous methods of making the mercury-sodium dispersion may be employed. The weight ratio of mercury:sodium as illustrated in Example 2 is 19.2:100 to 48: 100, but it is apparent that smaller quantities of mercury also exert a beneficial eflect. Moreover, the process of the invention may be carried out either continuously or batchwise. If desired the dispersion of metallic sodium or sodium-mercury maybe contacted with the gas countcrcurrently in a suitable tower or other apparatus designed for the purpose. Any suitable method may be employed for collecting or recovering ethylene from the product obtained in the practice of the invention. If desired, such purified ethylene may be fractionated at low temperatures, for final purification.

Since many diflerent embodiments of the invention may be made without departing from the spirit and scope thereof it is to be understood that I do not limit myself except as set forth in the following claims.

I claim:

1. A process for the purification of ethylene containing acetylene as an impurity which consists in passing the said ethylene at a temperature of about 30 to 150 C. through a dispersion of metallic sodium in a liquid hydrocarbon medium to which has been added a sumcient quantity of anthracene to prevent the formation of foam recovering the ethylene from the gaseous product, and purifying the said recovered ethylene by distillation.

2. A process forthe purification of ethylene containing acetylene as an impurity which consists in passing the said ethylene at a temperature of about 30 to 150 C. through a dispersion of sodium amalgam in a liquid hydrocarbon medium to which has been added a sufficient quantity of anthracene to prevent formation of foam, the weight ratio of mercuryzsodium in the amalgam being from 19.22100 to 48:100, recovering the ethylene from the gaseous product and purifying the said recovered ethylene by distillation.

3. A process for the purification of ethylene containing acetylene as an impurity which consists in passing the said ethylene at a temperature of about 70 to 110 C. through a dispersion of sodium amalgam in a liquid hydrocarbon medium containing a suficient quantity of anthracene to prevent the formation of foam, recovering the ethylene from the resulting product, and purifying the said recovered ethylene by distillation.

e. The process of claim 3 in which the said liquid hydrocarbon medium is a tetrahydronaphthalone-naphthalene mixture.

5. A process for the purification of ethylene containing acetylene as an impurity which consists in passing the said ethylene at a temperature of about to C. through a dispersion of metallic sodium in an alkyl naphthalene containing a sufilcient quantity of anthracene to prevent the formation of foam, and thereafter recovering ethylene from the resultant product.

FRANKLIN S. CHANCE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,801,412 Carlisle Apr. 21, 1931 1,862,003 Carlisle et a1. June 7, 1932 1,939,839 Williams et al Dec. 19, 1933 2,378,969 Bailey et a1. June 26, 1945 2,413,254 Soday Dec. 24, 1946 FOREIGN PATENTS Number Country Date 264,245 Germany Sept. 9, 1913 

1. A PROCESS FOR THE PURIFICATION OF ETHYLENE CONTAINING ACETYLENE AS AN IMPURITY WHICH CONSISTS IN PASSING THE SAID ETHYLENE AT A TEMPERATURE OF ABOUT 30* TO 150*C. THROUGH A DISPERSION OF METALLIC SODIUM IN A LIQUID HYDROCARBON MEDIUM TO WHICH HAS BEEN ADDED A SUFFICIENT QUANTITY OF ANTHRACENE TO PREVENT THE FORMATION OF FOAM RECOVERING THE ETHYLENE FROM THE GASEOUS PRODUCT, AND PURIFYING THE SAID RECOVERED ETHYLENE BY DISTILLATION. 